why is the lack of "fur" positive Progression for humans?

Hi, Arrogantape.Welcome to EvC! Although "prove" is a strong word, there actually are ways to provide evidence for your hypothesis.First of all, evolution cannot work as a contingency plan. New features don't become fixed in populations "just in case." Natural selection can only push "plan A": that is, it works for things that are crucial, not for things that might be handy. That's why evolution tends to produce specialists.So, since the genus Homo (and its pregenitors) appears to have arisen on the arid savannahs of Africa, you're going to have a very hard time explaining what selective pressures led to an aquatic lifestyle.----- But, our heads, which presumably go first while swimming, still grow hair. If the loss of hair is for streamlining, shouldn't our head hair have been the first to go? Badgers and bats and possums have adipose fat too. Does this mean they are aquatic? My baby doesn't.

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-BluejayDarwin loves you.

Hi, arrogantape. Care to throw your baby in the water to prove it?On the website linked by Chiroptera earlier (Aquatic Ape), there is a page that addresses the reason why people think babies can swim. Basically, it is a misreading of an old (1939) scientific paper recording the behavior of mammals in water, which concludes that human infants move in the water in exactly the same manner as other young quadrupeds. Moore (the website guy) has this to say about it:

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So that's the sad secret of the drowning infants; what we actually find here is not so much "swimming babies" as infant mammals slowly drowning without a struggle.

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----- Also not true. Again, see the site Chiroptera linked for a refutation of this idea.-----Anyway, the topic of the thread is "fur/hair," not swimming or adipose tissue, so, let's talk about hair: And this tells us that there are other factors that are more important in regards to hair than aquatic streamlining. You yourself have put "body odor" as more important than hydrodynamics.

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-BluejayDarwin loves you.

Hi, arrogantape. Did you even read the link, or even my comment in Message 68? Here's what you would have seen if you had:

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They always seem to mention the human infants and how their movements are usually "rhythmical and organized" and are "ordinarily sufficiently forceful to propel the baby a short distance through the water". So far so good. But they don't seem to ever mention the fact that the same study looked at other mammalian infants (opossum, rat, kitten, rabbit, guinea pig, and rhesus monkey) and found that they behaved the same way: "these rhythmical movements of the human infant are quite similar to those of other young quadrupeds in water".

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I guess it's my fault for not providing this particular quote in my message, but I did provide a link to it. The little commentary on Moore's site is really just a tiny blurb, so I thought it wouldn't be too much trouble.Please note that another primate (rhesus monkey) was also tested in the same study and showed the same behaviors as human infants. So, please stop asserting that human infants are somehow unique in this ability without showing evidence that overturns my evidence.And, maybe babies know how to hold their breath because they lived in an aquatic environment for the first nine months before parturition, and didn't breathe through their mouths during that time.----- Most mammals from hot regions have fur: warthogs, lions, hunting dogs, anteaters, bats, bears, water buffalo, antelope, camels, zebras, capybaras, lemurs, tarsiers, etc. (The ones in bold are mammals with significantly thicker fur than primates.) Clearly, the presence of fur has nothing to do with climate.Please also notice that elephants and rhinos and naked mole rats have lost their fur. None of these did so for hydrodynamic purposes. Australopithecus could probably outrun a bonobo, in terms of both absolute speed and endurance.
-----By the way, if you put "qs=Person's Name" inside brackets [ ], then cut and paste the quote, then follow up with "/qs" in the same brackets, you get this: You can push the "peek" button at the bottom of a message, and it will show you all the formatting and hyperlinking codes in that message.

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-BluejayDarwin loves you.

Hi, Ape. Okay, here's a quote from the other link that I provided in Message 68:

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Morgan uses Pond's observations that humans are on the fat end of the scale compared to other mammals as her basis, but ignores Pond's observations that both quantity and amount of fat in humans is similar to that of captive monkeys if they aren't kept on a strict diet.

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So, there is nothing unique about human fat that point to a special adaptation to water. If you want to argue fat, you must understand that your argument also supports an aquatic origin for all mammal taxa.Also, there is nothing unique about our natural swimming instincts, either.So, what's left? Long legs and no hair.These two are just as easily explained as a running adaptation as a swimming adaptation.Also note that no truly aquatic mammal has long legs (you might could make a case for the capybara, but that's a bit of a stretch). In fact, no truly aquatic vertebrate, extant or fossil, has/had long legs. Every aquatic vertebrate has/had an elongated body and shortened hindlimbs, probably because long hindlimbs would increase drag. Free hands.And better running ability than its forebears.

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-BluejayDarwin loves you.

Hi, Ape. It was just some helpful information. It just makes the dicussion easier to follow.Also, if you use the "Reply" button at the bottom of a message instead of the "Gen Reply" at the bottom of the page, the message appears as a response to that message, and lets people know who you're replying to. Some people are set up to receive E-mail notification when a response is written to them, and they don't get that notification if the response isn't attached to their message.----- I don't believe that chimpanzees and gorillas can outrun humans (on average, and assuming non-couch potato humans, of course).I found one study, here, that puts maximum human running speeds at just under 8 body lengths per second, and gorillas at less than five and a half. Using the body lengths given in the study, that puts humans at around 24 mph, and gorillas around 20 mph.Of course, they probably used an Olympic record for the maximum human speed (my university doesn't have a subscription to the paper where the numbers for this study came from, so I don't know), and average speeds would probably be more informative than maxima, anyway. However, I'm confident that the average human today is a poorer runner than our Paleolithic forebears. But, there would be an obvious survival advantage to being able to carry one's child while running. Clearly, though, she did survive. I like to think Australopithecus could have waved its arms around while running to scare vultures off carcasses or even startle predators. Standing up makes you look bigger than you really are.Of course, the topic is hairlessness in humans, and we seem to have gone quite noticeably off that topic. Perhaps we could open up a new thread about aquatic vs cursorial Australopithecus?

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-BluejayDarwin loves you.

Hi, Ape. Don’t take anything I say personally (unless it’s obviously mean to be personal): you should know that scientists are all about beating up on each other’s theories. That’s the whole point. I apologize if what I said was offensive to you.----- Well, there is also no refuting that our longer, skinnier fingers fit in smaller holes than a gorilla’s, but that doesn’t mean they were made for picking our noses.Have you ever looked at a horse? I can only imagine that a primitive man, seeing how fast that horse can run, really wanted to know what it felt like to be moving that fast, and, seeing how long and flat that horse’s back was, thinking that that horse was just begging to be sat on anyway. There’s no doubting that the horse’s physiology is nearly perfect for use as a mount, but that doesn’t imply a causative link. I disagree: I don’t see how the human foot is specialized for locomotion in water. It doesn’t really look like the foot of anything that lives in water, as far as I can tell. In fact, I think it looks a lot more like the foot of a wolf or other cursorial mammal’s than an aquatic animal’s foot:

• The foot is elongated between the ball and the heel, allowing greater leverage in a running step. This is a trait common to felines, canines and theropods, but not seen in beavers, whales, platypuses, otters or seals.
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• The toes are short, so they don’t break or make the step awkward (again, like the felines, canines and theropods, but not like aquatic mammals, which usually have long toes for walking in soft mud or for supporting a webbed foot).

Of course, our feet aren’t nearly as cursorially advanced as the canines’, felines’ or theropods’, but we had to compromise our running ability with our bipedal balancing ability, so that rather well explains the inconsistency there, I think. How would swimming bridge the gap between brachiating and walking upright? I don’t see any sort of connection here.

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-BluejayDarwin loves you.

Hi, Ape.On the subject of "floodplains": You and RAZD have made counter-assertions. In this, RAZD has the advantage, because your argument relies on the term “floodplain,” and RAZD has shown that the term doesn’t always mean what you think it means. Now, one of you should present some evidence about the "floodplain" of eastern Africa ~5 Mya, because only case-specific evidence is going to resolve this issue.----- There’s an obvious disjunct here: Lucy is helpless on the plains, but she can neutralize crocodiles in the water? I don’t buy that at all.

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-BluejayDarwin loves you.

Hi, Ape. Yes, they do. They call it the "terrestrial ape hypothesis." Basically, it states that the hip and pelvic structure are adapted for walking on the ground.A specific flavor of this model (with a couple variations) has been presented in this very thread: free hands while walking (for carrying food or young or for brandishing sticks or scaring predators).There is also the tree-walking hypothesis: bipedal, upright locomotion actually evolved for walking along tree branches (this is obseved in orangutans), and was thus a "preadaptation" for terrestrial locomotion. I thought hanging in trees was ruled out in the bipedal creatures by both the terrestrial and aquatic ape hypotheses. I don't think this is a viable idea: if you're living near the water, you're living near crocodiles. The crocodiles will generally go wherever you go if they want to eat you.-----I think you've misunderstood some of what the aquatic ape hypothesis says. It doesn't say anything about swimming or aquatic locomotion, just that upright walking was originally used for wading. Like RAZD, I won't say that our ancestors didn't wade, but I will say that it was not the underlying mechanism of hominid evolution: we are not adapted to a true aquatic lifestyle. Swimming adaptations are not posited by the aquatic ape hypothesis, and are not upheld by the evidence, anyway.Remember the foot argument I made in Message 90?: This is clear evidence of a cursorial history, and is very difficult to rationalize with a wading or swimming history, even though I have found proof here that chimpanzees wade. I bet not.

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-BluejayDarwin loves you.

Hi, Ape.Welcome back. It’s good to see you(r words) again.I have not spent much time thinking about the Aquatic Ape Hypothesis since you last left us, but your return has prompted me to think about it a little bit more. I am not so antagonistic to it as I was before (though I still reject it at the current time).First off, even though the flat foot is off-topic for this thread, I wanted to mention it peripherally. Only Homo floresiensis has flat feet among the genus Homo: can this really be seen as anything more than evidence that the hobbit was aquatic? How does it suggest that our ancestors were aquatic, when the adaptation appears after the emergence of our species?-----But, to get back on the topic of nakedness, I don't understand why nakedness points to an aquatic origin. The only naked aquatic mammals are cetaceans: all other aquatic and semi-aquatic mammals have fur.It seems that, in every case, mammals adapting to an aquatic lifestyle developed webbed toes, flippers, blubber, and/or closable nostrils before they lost their fur.For example, consider the following: beavers and muskrats, otters, seals, the water opossum and even the platypus. All of these are semi-aquatic or aquatic mammals, yet all of them still have their fur. Is there a reason for hypothesizing that aquatic apes are an exception to this trend?It seems that, if hairlessness in apes is to be explained as an aquatic adaptation, the lack of flippers, blubber, and closeable nostrils would all be found wanting an explanation. Thus, wouldn’t it be more parsimonious to explain the lack of fur as a way to shed heat on the savannah?

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD. Looking at this from a genetics perspective, I don't think this statement is accurate. According to Wikipedia, sexual dimorphism in body hair pattern is due to the activity of androgens, which produce more body hair in males.If Wikipedia is correct, then there seems to be at least two different genetic mechanisms at work, one that explains the sexual dimorphism, and one that explains the difference between us and the other apes.These two mechanisms need not even be linked at all. So, I don't think Ape actually has to explain the dimorphism in order to explain the "hairlessness."

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD. It shows a mechanistic distinction between dimorphism and "hairlessness." Whether or not the two mechanisms are linked is now the question that should be addressed.----- This would be true, no matter what the original cause was. There is currently no strong selection pressure on thermoregulatory ability or swimming ability, either, which is equally compatible with the existing variation in hair pattern.----- This could get into a chicken-and-egg scenario: we could just as easily have become "naked" first by some other mechanism, and only afterwards have associated "nakedness" with female sexuality because of the differences due to hormone activity.----- How can I answer the question, "Why didn't X happen?"Why didn't snakes on the African savannahs develop rattles to warn ungulates not to step on them, as snakes in North America did?However, since the development of terminal hairs seems to be tied to male hormones, total nakedness would seem to incur reproductive costs on males. Thus, the existing pattern may be a compromise between thermoregulation and hormonal requirements for reproduction.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD. And females that are hairier than I am are also fairly common in the population.Over 170 genes are involved in hair morphogenesis(according to this abstract, anyway): you can't expect there to not be noise.----- Except that, curiously enough, the difference is known to be caused by androgens. That's why "androgenic hair" is the technical term for the hair that men grow and women don't.-----I have nothing against a sexual selection explanation for hairlessness, but the simple observation is that there are two factors involved: one makes all humans "hairless," and another makes males grow extra hair.So, there is some mutation that causes both sexes to be equally hairless, which is what you've been asking Drew to produce. But, there is a second genetic mechanism involved, which is a side effect of male hormones. This second mechanism is acted upon by sexual selection. But, this does nothing to show what the first mechanism was for.In fact, it is consistent with all three hypotheses so far proposed. The aquatic ape hypothesis is faulty for other reasons, but the thermoregulatory hypothesis is still intact.I am not advocating any one of these models, but I think it should be acknowledged that the dimorphism and the "hairlessness" are not necessarily the same question, and no evidence so far presented is able to link them. Your evidence still has not explained the first mechanism.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD. Lots of things could have been, but aren’t. You can’t make an argument about evolution from what didn’t happen unless you accept teleology as a valid explanatory framework.The fact is that one mutation did happen, and it would have worked well enough: there’s no reason to think that something else should have happened. You don’t need bare skin to improve the efficiency of perspirative cooling over hairy skin.Besides, I can turn it back on you: If the fact that we’re not completely bare disproves the evaporative cooling hypothesis, then how does the fact that men are generally less attracted to 12-year-olds than to 20-year-olds not disprove sexual selection for younger-looking females?You don’t have to take everything to the extreme to make it work.----- If you take away a male's ability to produce or respond to androgens (testosterone specifically, I think), you get a male (usually underdeveloped and feminized) with female pattern body hair (here is Wikipedia on the subject). So, the dimorphism in hair pattern is due to a hormonal mechanism. That the non-androgenic pattern of body hair in humans is different from the typical pattern for other apes shows that something else (independent of androgenic dimorphism) caused our hair’s development to be arrested before the terminal stage.It might be sexual selection for younger-looking females that is secondarily inherited by males.
It might be natural selection for increased efficiency in perspirative cooling.The obvious answer is that the dimorphism does not need to be explained by whatever this mechanism turns out to be, because the dimorphism already has an independent explanation that can very readily and easily be observed.So, you need to produce evidence other than dimorphism to show that our relatively underdeveloped hair is due to sexual selection.-----That males have no stabilizing selection for a specific amount of body hair is also meaningless, because we haven’t lived on the savannahs for a long time. However, I would like to point out that there is a difference in mean hairiness between African and Caucasian men, which is consistent with the savannah hypothesis.It could indicate that Caucasians started growing more hair after they went to Europe, or that there was continued selection in Africa for males to be less hairy (either sexual or natural selection may be the case). But, whatever the case, it is not explained by sexual dimorphism.----- What features evolved before the savannah ecology?
And, what do these features have to do with the loss of terminal hair in humans?----- Why doesn’t the observation that dogs, hyenas and cats don’t sweat fully explain the disparity?Homo is the only alleged cursorial hunter on the savannah that uses evaporative cooling as a major thermoregulatory mechanism on its entire body, and thus, is the only cursorial hunter who stands to gain thermoregulatory advantages from losing its terminal hair.The appeal to other cursorial hunters as negative evidence fails.----- You’re talking to Bluejay now, not Arrogantape: I have already rejected the aquatic ape hypothesis.Note also: I acknowledge that there is no loss in the number of hair follicles. However, I will continue to use the terms hairless, bald and hair loss (always in quotation marks) to refer to the defecit of terminal hair, because underdeveloped hair and arrested development of terminal hair make very awkward sentences. But, know that this is not a point of contention between us.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD.Sorry I'm taking so long on this. I'm trying to get a reply together, but it's turning out to be a lot more work than I really want to put in to EvC, and my field work is starting to pick up now that the rain is gone.But, I'll have some stuff to present soon (probably not nearly as spectacular as I want it to be, though).Thanks.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.

Hi, RAZD.Sorry I took so long on this: it took me this long to solidify my thoughts.Here is my argument against sexual selection as the mechanism for hairlessness in humans:Human males do not have a random distribution of body hair patterns. Asian males are predominantly hairless, and Caucasian males are predominantly hairy. African males are intermediate, having both hirsute and bare patterns. This 1960’s study has the hairiest and barest chest hair patterns being the two most common groups in African American men, creating a bimodal pattern, which could suggest disruptive selection, in which both hairiness and bareness are selected for.Interestingly, when you look even closer, you see a different picture. The earliest living branches of humanity, the Khoisan and Pygmies, have very bare-chested males (Google "Khoisan people" or "pygmies" and count how many hairy-chested males you see: none of them wear shirts, so it's easy to tell), and it’s actually the later-branching groups that account for the hairiness in African males. This implies that bareness is the initial condition for male Homo sapiens, and that hairiness in males is atavistic. Thus, the atavistic hairiness of males explains the dimorphism, not the hairlessness of females.Thus, while sexual selection for bare skin seems to be prevalent today, and may very well be the cause of sexually dimorphic hair patterns in Caucasians, it couldn’t possibly have been the primal cause, because early Homo sapiens were not sexually dimorphic in terms of body hair patterns.

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-Bluejay (a.k.a. Mantis, Thylacosmilus)Darwin loves you.